1. Field of the Invention
This invention, which is an extension of the method and apparatus disclosed in application Ser. No. 07/497,543, now U.S. Pat. No. 5,005,973, filed Mar. 20, 1990 in the name of the present inventors relates to a method and apparatus for boresighting such aimable units or components as weapons systems and avionics equipment aboard fixed-wing and rotary-wing aircraft as well as tanks and other vehicles to thereby insure that a weapon's delivery point coincides with its aimpoint. Through the use of optical metrology, the various components are boresighted to maintain alignment relative to the aircraft boresight reference line. Specifically, this optical metrology system accomplishes boresighting through the transfer of a fixed reference line in yaw, pitch, and roll from a measurement reference line on aircraft or other vehicle to various points including sighting stations, sensors and weapon stations. For example, it is necessary that various modules on both rotary and fixed-wing aircraft maintain correct positions within 30 arc seconds or less. Through use of the boresighting system of the present invention, departures from the prescribed position can be measured and corresponding corrections effected.
Typical modules include a heading and attitude reference system, gun, stabilized sight unit, night vision unit, doppler radar, air data sensor, missiles, head-up display, forward looking infrared and laser spot tracker.
2. Prior Art
Alignment devices have been employed in the past to verify boresight alignment and to measure boresight error between a reference line of sight and the sighting means of the vehicle and a weapon on military aircraft and other vehicles.
One such system is that of U.S. Pat. No. 4,762,411 which shows a boresight alignment verification device comprising a portable cart spaced apart from the air-craft which carries the sights and weapons to be bore-sighted and employing a collimated light source and an extendible periscope which directs light to an optical reference fixture mounted at a line of sight on the aircraft. The reflected light is matched on a matrix camera against a beamsplit portion of the projected light. This arrangement has the disadvantage of relative movement occurring between the spaced-apart verification means during the frequently lengthy calibration period and corresponding repositioning, in contrast to applicant's system in which the verification means is attached to the aircraft and is not relatively movable thereto.
U.S. Pat. No. 4,191,471 shows an aircraft armament alignment arrangement employing a jig which is temporarily fastened to the aircraft. A collimated, incoherent light source is attached to the aircraft at a reference surface which defines an aircraft datum line. A collimator fastened to the jig carries a translucent screen with grid markings on which the image of the light source is visible. The jig is moved relative to the aircraft until the image is centered and is there fixed. Thus, the jig becomes an intermediate element for carrying directionality and alignment information to a weapon bore and to a sight. The collimated light source is next attached to produce a beam parallel to the bore of a gun pod and the gun pod adjusted so as to center its light beam on the screen of the repositioned collimator. The collimated light source is then moved to a socket on the jig and its light beam directed to an optical sight. The latter is then adjusted until its line of sight is parallel to the axis of the collimated light source. Factors detracting from the potential accuracy of this system are errors resulting from the use of an intermediate element and the repositioning of the light source and the collimator.
U.S. Pat. No. 4,769,539 shows an arrangement for the measurement of the relative roll angle between a two-beam sending unit and a bi-cell receiver. The two light beams passing through apertured masks are differently modulated, and when received on the bi-cell the resultant currents are separated electrically and the roll angle computed from the ratios of these separated components. The light beams fill their corresponding masks, and the light passing through the masks is imaged by a lens onto the bi-cell. U.S. Pat. No. 4,769,539 will operate at one separation only between sending point and receiving point without refocusing of the sending unit optical system. The smallest measurable change in roll angle (the noise equivalent roll angle increment) depends on the size of the masks on the bi-cell; smaller images give superior resolution. The range of roll angle measurable, and especially the linear range, also depends on the size of the images of the masks on the bi-cell; larger images give superior roll angle measurement linear range. A difficult trade-off between resolution and linear range of measurement may need to be made in applying the teaching of U.S. Pat. No. 4,769,539. The sensitivity of roll measurement also depends on the distance separating the mask images on the bi-cell. This separation, along with the sizes of the mask images, reflect the result of making the required trade-off to achieve the resolution and range of any particular application. The movement of the images in yaw, for example, depend on the yaw angle of the sending unit and the distance between sending unit and receiving unit. This yaw error must be very small compared with the roll measurement range or the mask images will move completely off the bi-cell dividing line.